Jetting w/xr50 carb???

[capturedbyrobots]

So I was helping Surfnturf with his 86 Aero the other day,
and it was running lean and bogging.. When he got the scooter
it had a stock XR50 carb bolted to the mani.
It ran great with this carb with it's jetting for all of summer and fall.
Plug looked perfect. and this was with an open filter and stock exhaust.

I checked the jetting yesterday, and it was very small. The jet said 58 on it.
This was a main jet??? Man that's small.
Weird.
On my 89 Jog, the stock carb came with a 90 jet.
We drilled his MJ out to about a 61-63 ish, and the bog went away and it ran like a top.

So my question is this.
How can this type of carb run fine on these motors with such a small jet?
Is it something about this particular carb style?

It is the type of carb that has only a replaceable main jet...
and has a fixed idle jet. Looks like a pocket bike carb...
It looks like this...

[bakaracer]

some engines require it to run a larger jets than others. its in the design in the intake and engine on how it wants air and how much.engine styles will vary in this.A good example is the af05 and af16 engines.both 50cc and the carbs are 14mm but use a totally different needle,jet and slide in the carb.

[drizzle]

some engines require it to run a larger jets than others. its in the design in the intake and engine on how it wants air and how much.engine styles will vary in this.A good example is the af05 and af16 engines.both 50cc and the carbs are 14mm but use a totally different needle,jet and slide in the carb.

...crap. different main jets?!

if so, i've wasted 20 dollars.

[bakaracer]

what size carb is that one?measure the opening that bolt to the manifold.That will tell you the size of the carb.

[surfnturf]

I haven't measured it, but specifications would indicate it being a 13mm carb.

[bakaracer]

If its a 13mm carb thats smaller than the stock carb that comes on your scooter.

[surfnturf]

I realize the 1mm size difference, but it runs well and seems to be as peppy as could be expected from a stock model. It has a Ruckus variator w/Elite SR weights too and easily exceeds 40mph. I think there is some trick to why this carb provides enough fuel with such a small jet. Possibly the open element filter is having an effect as well, but it still seems like there is something different about it from the stock carb (aside from the manual choke).

[capturedbyrobots]

Perhaps it's because it's a carb meant for a 4 stroke bike?
Could that make a difference?